1. Field of the Invention
The present invention relates to the art of fluid conduits, and more particularly to the construction of restored fluid conduits in place having greater structural strength than the pre-existing original fluid conduits.
2. Description of Related Art
Waste water and sewerage frequently are conducted through fluid conduits of concrete, brick and similar porous material. Conduits deteriorate for various reasons, including hydrogen sulfide related corrosion. Conduits, including concrete and steel structures, corrode with consequent loss of strength, and must be quickly repaired cost effectively for the long term. See, generally, “Sulfide in Wastewater Collection and Treatment Systems,” Ch. 2, American Society of Civil Engineers (1989).
Herein in this specification for simplicity of explanation, the term “conduit” will be used to mean and include conduits, pipes, box tunnels, culverts, and enclosed containers, pump stations and wet wells and the like, unless the text herein indicates otherwise.
The sewer infrastructure is such that it is often desired and sometimes necessary to restore or refurbish existing deteriorated sewer conduit rather than construct new sewer conduit. In the past, several modalities have been used to restore existing but deteriorated sewer conduits. One method, for example, is to remove the earth above the sewer, and construct a new conduit parallel to, or in place of, the old structure. Such a method necessarily involves great inconvenience to people using the roads, buildings and other structures which were made unusable during such a restoration project.
Another modality is to apply fresh concrete within the conduit to the interior surfaces of the conduit that have eroded. Such a method results in a conduit no better than the one corroded in the first place. Further, the timing during the usual daily cycle of sewer flow, when such repairs usually are made, becomes a problem where the repair must be made while the sewer is in ongoing use. The length of time necessary for concrete to set is substantial, which forces any restoration project to be performed in limited stages. Thus, fresh concrete is applied to a limited length, or to only a portion of the inner circumference, of a conduit during the first night's work, and allowed to set. The workers and their various tools, vehicles, etc. must evacuate the conduit until the next night's work window in the daily cycle when the workers can re-enter the conduit. In the interim time between these work windows, that is, during the day, the waste water level will have risen, often filling up the conduit to, or near to, the crown, leaving various deposits and/or contaminates on the freshly poured or set concrete. During the next successive night's work, fresh concrete is poured to adjoin the previous night's application, but there will be these contaminates and deposits like a thin film covering the interface surfaces with the concrete of the previous night's application. The interface between the two applications is sometimes called a “cold joint.”
Another method for restoring a conduit is described as “slip lining,” where a new pipe is inserted within the old conduit. Such a method necessarily reduces the interior diameter of the conduit. Further, problems are presented when encountering connecting lateral pipes and like anomalies in the sewer lines.
Another method of restoring existing sewer conduit has been taught in which a corrosion resistant layer of material, such as polyvinyl chloride is positioned within the corroded conduit, where the layer has widely separated spikes and/or ribs, including “T” shaped spikes or ribs, formed on the side or surface facing away from the conduit interior and through the corroded conduit. The polyvinyl chloride layer is supported in position while fresh concrete or other setting material is poured between the layer and the corroded conduit. The setting material, such as, for example, concrete, surrounds the “T” ribs or spikes before setting, and in ideal conditions forms a mechanical connection between the polyvinyl layer and the newly set concrete. In such a system, however, the connection between the polyvinyl chloride layer and the newly set material is purely mechanical. Further, the area of connection is limited by the area of the overhang of the top of the widely separated “T” shaped ribs or spikes, typically approximately five percent of the total plastic area being held. Further still, any load transfer from the top of the existing conduit from the conduit to the polyvinyl chloride, in the best of configurations, aside from friction, is limited by the geometry of the rib or spike structure; that is, such load must pass from the shank or pole of the rib or spike.
In the past, as a solution to such problems, it has been taught to place a sheet of lining or layer of polyvinyl chloride layer over a traveling, collapsible form movably positioned inside the conduit. When positioned, the form is expanded, pushing the lining or layer into position to have grout or cementitious material inserted between the lining, or layer, and the conduit's inside wall. Such restoration projects necessarily require specially constructed vehicles to carry and position the collapsible forms, and rely on cementitious repair materials which are also subject to corrosion. Repairs with a single plastic mechanically anchored, non-bonded lining material are subject to punctures and seam leaks, which expose the underlying repair material or original substrate to corrosive gases and liquids. This can result in separation of the lining material from the substrate and could result in a catastrophic failure, including a separated lining material clogging the conduit.
Another method employs a non-mobile construction framework within the conduit, which supports or holds the lining or layer in place while the cementitious material is inserted between the lining, or layer, and the conduit. In all of these methods where cementitious material is built up within the conduit, cold joints result not only between the cementitious material and the conduit, but also between the successive insertions of the cementitious material.
Other methods of restoring corroded conduit by positioning a sheet of material inside the conduit involve the insertion within the conduit of a tube, sometimes inverted, of polyester or vinyl ester saturated felt-sock or like material, or folded thermoplastic material. The tube within the conduit is pressurized to expand the tube to be in contact with the interior of the conduit. Then, heat is applied to commence a setting process. There is little or no chemical bonding between the tube and the host conduit. The resulting restored pipe has little added to the strength of the pipe from its deteriorated, weakened pre-restoration condition, since the added layer or sheet must be thin enough, or at least flexible enough to respond fully to the inflating pressures expanding the tubular layer out to the inner surface of the conduit.
Some of these systems have a sheet of inner lining or polyvinyl chloride layer primarily to provide resistance to the corrosives in the conduit. Also, some of the systems require significant elaborate devices and complicated removable support devices to complete the installation. These labor intensive devices include pressurization, traveling mobile collapsible forms, or non-mobile framework that has to be constructed in place. All such devices must be brought into the conduit and removed from a conduit after the work is done through limited access, such as manholes and hatches.
In many conduit restoration projects, it is preferred to temporarily by-pass the old conduit or perform the work while the sewer is operational. The temporary by-pass, if possible, is extremely expensive, environmentally risky, and disrupts surface businesses and street accesses. Normally, sewer flow is minimal during the hours between midnight and around 7:00 a.m. o'clock, and increases dramatically thereafter. Thus, during the entire optimal time allowed for restoration work, a period of approximately seven hours, workers must go to location within the sewer network, set up the various expanding or pressurizing apparatus and/or the frame works, preform the positioning and material application procedures, allow time for the concrete or other material to set, dismantle the construction apparatus, and then evacuate from the sewer network. However, cementitious material, such as typically concrete, requires substantial time for setting, and cold joints are inevitable. Restoring the corroded conduit with cementitious material has always had timing, performance or scheduling problems.
In the past, another method for restoring corroded concrete conduits has been building up the cement concrete behind a plastic lining layer having “T” shaped ribs or spikes. The cementitious material is inserted in the space behind the layer or lining. Because of the timing problems as described, the concrete cement can be filled between the plastic lining layer and the corroded concrete wall only to a certain height before time must be allocated for it to set. Next day, additional height is added during the permissible time window by pouring more concrete behind the polyvinyl chloride layer. The interface between the first and second nights' pouring inevitably is a cold joint, with all of the problems such a joint inherently has.
The amount of height added each day, often referred to as a “lift,” is determined and limited, also, by the weight of the cementitious material which the layer or lining can support. Cementitious material weighs, typically, as much as 155 pounds per cubic foot. The layer of polyvinyl chloride, typically, is relatively thin, relatively flexible and incapable of supporting such weight if unsupported with elaborate devices or procedures. For example, various positioning and supporting apparatus, which are bulky and difficult to transport to location within the sewer network by virtue of such weight, must be installed or constructed within the conduit to hold the plastic lining layer in proper position while the concrete is poured behind it and sets, or the cementitious material is pumped in time-intensive lifts. Further, the problems associated with this procedure normally require that only a certain, less than complete height of concrete be poured and set behind the plastic lining layer each night, leaving substantial portions of the space between the conduit's inner wall and the polyvinyl chloride layer exposed to the waste water “flush” during the day of the sewer daily use cycle. As noted, such a “flush” leaves deposits or a thin film of contaminates on the back surface of the polyvinyl chloride facing the conduit's inner surface. This “flush” also leaves such deposits and contaminates on the surface of the concrete conduit. These deposits and contaminates will interfere with any bonding that may be desired between these filmed surfaces and the fresh concrete poured into the space between the plastic liner and the conduit inner wall surface.
In all of the methods discussed herein above, the plastic lining or layer is not designed to have any connection or fastening to the cementitious material between it and the conduit except by virtue of such mechanical locks as the “T” shaped ribs or spikes, or by bolts. The structural integrity of the interior of the conduit after restoration is maintained mainly by the new cementitious material supporting itself after setting, and the polyvinyl chloride layer or lining supporting itself, except by the periodic fastening by virtue of the ribs, spikes or bolts. The tensile strength of the cementitious material is relatively low, on the order of ten percent of its compressive strength. Throughout the repaired circumference, stresses are not optimally distributed and are poorly transferred between the old conduit and the new repair. Since there is no evenly distributed, universal bonding between the polyvinyl chloride layer and the cementitious material behind it, any corroding substance that penetrates the lining or layer can and usually will begin deteriorating the cementitious material behind that layer, in the same way that the concrete conduit became corroded in the first place. Consequently, any breach in that layer or lining will commence the deterioration process anew, causing the layer or lining to separate from the cementitious material behind it and to collapse.
It has also been taught also to restore such conduits by application of corrosion resistant or corrosion proof polymers to the interior surfaces of the corroded conduits. See, for example, U.S. Pat. No. 4,792,493 to Vernie L. Belcher and myself. Further, it has been shown how such a deteriorated conduit can be given additional strength, enough so that the resulting conduit after restoration is very substantially more strong and more resistant to chemical etching by the waste water bacteria and acids than the conduit. See, for example, my U.S. Pat. No. 5,268,392 and No. 5,389,692, the specifications of which are incorporated herein as though fully set forth. Such linings and coatings, even for the entire circumferential surface area of the conduit's interior surface can be applied quickly, and set within the time windows permitted in the usual sewer daily cycle, as explained in my earlier patents. Such methods as have been known, however, usually are achieved by applying the restoring materials, usually co-polymers, to the corroded conduit interiors, and building up the thickness of the materials to the desired thickness. Achieving precise interior dimensions of the final product can be difficult, however, and requires careful attention in the application procedure.
It is still desired to provide a method of restoring a corroded conduit, so that the resulting structure has precise, predetermined structural dimensions. It is desired, further, to provide a method of restoring corroded conduits which fully utilizes preexisting structure and incorporates it into a new composite structure having greater tensile, compressive and flexural strengths than possessed by the conduit as originally constructed. It is yet further desired to provide a method of restoring existing corroded conduit that results in a unified, integrated composite structural material. It is yet further desired to provide a method of restoring a corroded conduit that results in an integrated composite structural material that has structural characteristics that are predetermined with respect to strength in tension and compression at pre-selected locations within the structural material. It is yet a further desire to provide a method for restoring corroded conduits that results in a structure that has a thermoplastic layer facing the interior that is evenly bonded to the material between it and the conduit and more evenly bears and distributes the load borne by the conduit throughout the resulting composite structure in the regions of the original conduit, the thermoplastic layer and the material between them which is impervious to hydrogen sulfide gas and other corrosives. The present invention meets these and other needs.